1. Field of the Invention
The present invention relates to a method of cleaning metallic films built up within thin film deposition apparatus, and in particular, it relates to a cleaning method for neatly removing substances such as metallic copper that have built up within thin film deposition apparatus during deposition.
2. Description of the Related Art
Chemical gas phase etching is a hitherto known cleaning method for the removal of metallic copper, for example. From a microscopic viewpoint, the process of chemical gas phase etching can be divided into 3 steps: a step for the production of an oxide film by oxidizing the metallic copper (metallic copper oxidation step), a step to produce a copper complex by complexing the copper oxide (copper oxide complexing step), and a step to sublimate the copper complex (copper complex sublimation step). In a cleaning method comprising these steps, a sequence of chemical reactions is performed in turn by the metallic copper oxidation step, copper oxide complexing step and copper complex sublimation step, whereby the metallic copper is removed by chemical gas phase etching.
Prior references to chemical gas phase etching can be found in the following: Examined Japanese Patent Publication (JP-B) No. H7-93289 (reference 1); A. Jain, T. T. Kodas and M. J. Hampden-Smith, SPIE2335, p. 52 (1994) (reference 2); M. A. George, D. W. Hess, S. E. Beck, J. C. Ivankovits, D. A. Bohling and A. P. Lane, J. Electrochem. Soc., Vol. 142, p. 961 (1995) (reference 3); and M. J. Hampden-Smith and T. T. Kodas, MRS Bulletin, p. 39 (June 1993) (reference 4).
Reference 1 discloses a vapor phase etching method for a thin metallic film on a substrate used in the production of integrated circuits, wherein the metallic surface of the metallic thin film is etched by contacting it with an effective quantity of a .beta.-diketone, or the like, that has been dispersed in an atmosphere that allows oxidation, and under conditions in which a volatile metal-ligand complex can form, and then volatilizing the metal-ligand complex. Copper may also be included in the metal that is etched. An embodiment is shown in which oxygen (O.sub.2) is used to oxidize the metal and hexafluoroacetylacetone is used as the .beta.-diketone.
Reference 2 describes an example in which H.sub.2 O.sub.2 is used to oxidize metallic copper. Hexafluoroacetylacetone is used to complex the copper oxide.
Reference 3 describes an example in which O.sub.2 remote plasma is used to oxidize metallic copper. Hexafluoro-acetylacetone is used to complex the copper oxide.
Reference 4 discloses a cleaning method for metallic copper as an example of a metallic copper etching technique involving the use of an oxidizing atmosphere and hexafluoroacetylacetone, which is a type of .beta.-diketone.
As mentioned above, chemical gas phase etching methods that use H.sub.2 O.sub.2, O.sub.2, remote plasma, or O.sub.2 to oxidize metallic copper are already known. It is also known that hexafluoroacetylacetone (1,1,1,5,5,5-hexafluoro-2,4-pentanedione), which is a type of .beta.-diketone, is widely used as a source material for complexing copper oxide.
When a process to deposit a metallic copper film on the surface of a substrate in thin film deposition apparatus is successively repeated while the substrates are replaced, a film of metallic copper builds up within the thin film deposition apparatus. When the film that has built up within the thin film deposition apparatus becomes thick, it causes problems with the deposition process, such as degradation of the films, and it is thus necessary to perform a cleaning process at suitable intervals to remove the built-up film.
However, the conventional methods mentioned in the above references are mainly concerned with the removal of thin copper films from substrates, and no cleaning methods have been proposed for the removal of metallic copper films that have built up within thin film deposition apparatus.
The present inventors have therefore tried to apply the chemical gas phase etching method mentioned in reference 1 for the removal of metallic copper built up within thin film deposition apparatus. That is, based on the chemical gas phase etching method of reference 1, copper oxide was produced by using oxygen to oxidize the metallic copper, a copper complex was produced by using hexafluoroacetylacetone to complex the copper oxide, and this copper complex was sublimated. However, with a chemical gas phase etching method based on the method mentioned in reference 1, the built-up metallic copper film became spongy (porous) and could not be neatly removed. Instead, problems occurred such as particulates or cavities forming in the lower surface of the built-up film, resulting in cracks in and flaking of the built-up film. The appearance of a built-up film that has become spongy is depicted in the photos of FIGS. 3 and 4, and the appearance of the flakiness is depicted in the photos of FIGS. 5 and 6.
As mentioned above, it has not been possible to use conventional chemical gas phase etching methods to neatly remove a film of metallic copper that has built up within this film deposition apparatus. Another paper (Mark A. George, Alan J. Kobar, Scott E. Beck, Jen Waskiewcz, Ron M. Pearlstein and David A. Bohling, "Chemical Vapor Etching of Copper for Cu CVD Chamber Cleaning," Advanced Metallization and Interconnect Systems for ULSI Applications in 1997, U.S. Session (Sep. 30, 1997)) regarding the results of research into cleaning methods for the removal of metallic copper built up within thin film deposition apparatus was also published very recently.
The present invention aims to solve the above mentioned problems and provides a cleaning method that can neatly remove metallic films of metallic copper or the like that have built up within thin film deposition apparatus without generating particulates or flakiness.